This disclosure relates generally to a method and system for color calibration of a display. More particularly, but not by way of limitation, this disclosure relates to a dynamic and adaptive display color calibration method and system in which points to be measured next in a color output space are determined based on actually measured color response values, so that the unique characteristics of the display can be accurately tracked during the color calibration.
Modern consumer electronic devices incorporate display devices (e.g., liquid crystal display (LCD), organic light emitting diode (OLED), plasma, digital light processing (DLP), and the like) to exchange information with users. Operation characteristics of the display devices may vary from device to device due to inherent properties of the display devices. For example, variations may exist in LCD components, such as backlight variations due to light emitting diode (LED) wavelength and phosphor concentration, color filter thickness, and the like. Thus, each display device may have slightly different color characteristics, white point, and the like.
A white point of a display device may be defined by a pair of chromaticity values (x,y) that represent a color produced by the device when the device generates all colors at full power (without any correction or calibration applied). For example, when red, green, and blue channels for a display device are all active at full power (e.g., maximum voltage applied from display driver to each of the red, green, and blue sub-pixels of the display), the chromaticity values, as measured in Cartesian coordinates x and y with respect to a chromaticity diagram, are the white point of the display device. White points may vary among display devices due to inherent properties such that when the red, green, and blue channels for a display device are all active at full power, the resulting (x, y) chromaticity value corresponding to the white point is different from the (x, y) chromaticity value corresponding to the white point of another display device when the red, green, and blue channels for the other display device are also all active at full power.
This native or original (uncorrected) white point of the display device may be corrected in a white point calibration process to be adjusted to a target white point which is consistent across multiple display devices. For example, the target white point may correspond to the D65 illuminant of the International Commission on Illumination (CIE). In the white point calibration, each device may be tuned (e.g., in a factory, or post-shipping during a calibration process) to the target white point by adjusting display control settings such as gain values for the red, green, and blue channels individually. Alternately, RGB adjustment values that produce the color (e.g., represented in a device-independent color space with target chromaticity coordinates (x0, y0) and target luminance Y0) corresponding to the target white point may be stored in a look up table (LUT).
In addition to white point calibration, the display device may be also subject to gray tracking calibration to faithfully reproduce the full range of gray levels from black to white (e.g., represented by the target white point) on the display device so that the shades of gray (e.g., linear range of R=G=B from 0 to 1) at different luminance levels will all appear to have the same neutral hue as the target white point (e.g., target chromaticity coordinates (x0,y0) for every gray level), and the highest luminance level of gray (e.g., target “white” color; target luminance Y0) will correspond to the brightness of the target white point. Accuracy of the gray tracking calibration using conventional techniques may depend on “good” balance between the native (uncorrected) response curves of each color channel (e.g., R, G, or B) of the display device (e.g., low or predicted non-linearity of electro-optical transfer function of the display). However, it is desirable to maintain high accuracy of the gray tracking calibration (or calibration of “gray” levels (e.g., luminance levels) of any color of interest) even in cases where there is excessive variation in the balance between the native response curves of each color channel of the display (e.g., high or unpredictable non-linearity of electro-optical transfer function of the display).